Marine organisms face a variety of challenges in their
quest for life and reproduction. They must obtain food for growth and survival,
avoid being food for other organisms, cope with the physical environment,
and have an effective strategy for bringing forth reproducing offspring.

Foraging
Ecology, the quest for food.

First we will look at Foraging Ecology, the quest for
food. Obtaining food is necessary for an organisms survival, growth and
offspring reproduction. Without food, almost nothing else about an organisms
relation to the world will matter for long.

There are many different strategies for obtaining the
necessary food. Organisms generally follow two basic strategies, being
either a generalist or a specialist. A specialist will prefer only a single
or few food types and a generalist will gladly eat many different food
types. Both of the strategies have their advantages and disadvantages.
A specialist may concentrate on a very nutritious food type; when it finds
it favored food, it will be able to obtain most of its nutritional requirements,
but it may have a hard time finding its favored food. A generalist may
be surrounded by many different edible food, but like spinach, it may not
be that good for the organisms, or it may take a long time to process the
food, such as eating barnacles with their hard shells.

Strategies for obtaining food

-Hunters, feed on larger, rarer organisms

-Browsers, feed on smaller, commoner organisms

Diet width and composition varied

-Monophagous, single food type SPECIALIST

-oligophagous, few food types SPECIALIST

-polyphagous, many food types GENERALIST

Different diet widths of five sea star species

Seastar species

#species of prey consumed

Percentage compositions of prey

Strategy

MEDIASTER

35

38,11,4,3, others <3

GENERALIST

CROSSASTER

26

47,13,11,5, others <3

GENERALIST

SOLASTER

9

23,15,13,10, others <10

GENERALIST

HIPPOSTERIA

9

99, others <1

SPECIALIST

DERMASTERIA

3

98, others <2

SPECIALIST

**Within one group of organisms (seastars),
there can be species that are either generalists or specialists.

There are three possible reasons why should
there be so much diet variation.

An organisms may have a preference
for a certain food type, and will choose it over other food types given
equal access to choices

Preference: Indication of foods chosen by a predator
given equal access to choices Average population preference study in food
choices of a sea urchin algal abundance avoidance preference Field Diet
**Equal Access to different algae, the sea urchin has preferred and avoided
food types

Diet preference in the gastropod Nucella over 4 weeks

Barnacel Food Type

Week 1

BBBBBBBB

Week 2

TTTTTT

Week 3

MMMMMMMM

Week 4

TBCBMBTBC

Barnacle food typesB-Balanus T-Tetraclita
M-Mytilus C-Cthalamus

**This study shows the gastropod Nucella
can have strong or weak preferences

Switching: Will an organism
switch preference with abundance characteristics? It may be to the advantage
of an organisms with a preferred food type to switch to another food type
if it becomes very abundant, but some specialists will not switch even
when surrounded by lots of great food.

Problem, under a given set of circumstances, how should
a predator forage? How should a predator respond to variation in environment,
such as patchiness of food supply. In such a case, what path should the
predator follow.

To solve this problem, ecologists have come up with a
model known as the Optimal Foraging Theory, in this model the predator
will completely avoid the unprofitable, and completely pursue the profitable.

The model has four assumptions: 1. Foraging behavior is
variable, and heritable. 2. Possible responses to prey are constrained
3. Most efficient foragers will be favored by natural selection 4. Efficiency
determined by maximizing energy gained in a set amount of time

Two types of consumers are defined by their Energy/Time
ratio (E/T).

1. Energy Maximizer: Fixed time to forage -maximize energy
gained in that time

As a starfish can only feed at high tide on the intertidal
zone, it is an energy maximizer.

The foragers face their first dilemma when they must decide
on the quality of the food item it will eat.

Specialist: maximal efficiency by eating only "best"
prey, but high time cost searching.

Generalist: low time cost, but lower efficiency because
it takes profitable and unprofitable prey.

Search Time VS. Time Spent Pursuing, Capturing, and Consuming
Prey searching time pursuit, capture, consumption time Time A B CPrey Species
D E

Optimal prey is the one where searching time and handling
time is minimized

**assume energy is the same, cost is time consumed

Energy Gained VS Time Handling for five prey species E
A D

Energy B Gained C

Time required to obtain and handle A--Best prey, most
energy gained per unit of timeE--Worst prey, least energy gained per unit
of time

Predictions from Model 1. Highest rank prey should always
be eaten. 2. Lower rank prey should be pursued and eaten only if this increases
net energy gain. Gains>Costs 3. Exception to 2, -Take lower rank prey if
recognition time is low low rank prey may be eaten if frequently encountered.
4. Predators should be more selective when prey are abundant and less selective
when prey are scarce. Search Time VS Handling Time of Scarce and Abundant
Prey scarce prey handling time Time abundant prey A B CPrey Species D E
Optimal shifts to the left when a prey species become abundant**assume
energy is the same, cost is time consumed

Energy Gained VS Time Obtaining + Handling 5 prey species
E D A Energy C Gained B Time required to obtain and handle prey Optimal
prey shifts to the right with increasing abundance 5. Inclusion of lower
ranked prey is independent of its own abundance and dependant on high ranked
prey abundance.

** This study shows that the snail will eat the best prey
first, and save the lousy prey for last. Inclusion of the lower ranked
prey is independent of its abundance and dependant on the abundance of
the highest ranked prey.

OPTIMAL PATCH CHOICE

The foragers second dilemma: How long should a forager
stay within a patch? If it stays too long it will be spending too much
time for the amount of energy it is accumulating.

**A predator should leave quicker in a low quality patch
than in a higher quality patch

Patch Quality Cumulative energy extracted t t t1 t2

**Time spent in a patch increases if travel time is long.

Reproduction Ecology

Reproduction is one of the primary goals of any organisms.
In order to keep a species from becoming extinct, its members must reproduce
at least enough offspring to replace themselves. Organisms invest a considerable
amount of time and energy into reproducing. The eggs and sperm they produce
are costly cells to make, and their only use is for reproduction. Some
organisms also invest a great deal of energy in mate selection and nest
preparation. In the case of the higher organisms, parental care may take
place, and the organisms will be investing its resources into its offspring
for even years to come. If an organism did not have to invest all of this
energy into producing and nurturing offspring, they would have more energy
available for investing into more complex organs allowing them to possibly
be better competitors in its environment. But reproduction is an absolute
necessity for organisms that are not immortal, and I do not know any that
are. Without reproduction, the species would be gone after just one generation.
Reproduction is not necessarily the most important thing to a particular
creature, it may be happy to just spend its time swimming and eating, but
it is the primary goal of the genes within the creature. The genes (the
instructions for creating an organism) are the only level that evolution
takes place. Good instructions for creating an organism that is good at
reproducing get passed on to further generations. If the instructions were
poor, the organism will not reproduce, and the instructions will be lost.
Only the good instructions get passed on. Natural selection is very much
at work at filtering out successful instructional strategies. One could
say that an organism is only the means to continue the flow of genes. That
is what natural selection has programmed the genes to do; to creature organisms
that deal with the environment well and reproduce. A gene that programmed
its organism to be poor at dealing with the environment would probably
not be passed on to the next generation. Only those genes that create organisms
that are successful in the environment get passed on. This filtering process
(natural selection) soon leaves only genes that are good at producing fit
organisms. If the environment stayed constant, then evolution would have
finished millions of years ago, but the environment is not constant. The
genes mutate every once in a few million reproductions. Most of these mutations
will be deleterious to the organisms that is created, but some may actually
benefit the organisms. Natural selection will work at filtering out the
good from the bad mutations. If the mutation is bad, the gene will probably
not be passed on (such as a mutation that hindered an organisms ability
to eat, the organisms starves to death and does not reproduce). A few of
the mutations may actually help the created organisms (such as a gene that
allowed for better sight, the organisms may be able to see food that others
were missing, or to avoid predation, giving the organisms an advantage).
A good mutation would quickly be passed on throughout the species population,
and this is evolution! Evolution selects for the best adaptive traits to
insure that each female replaces herself within her lifetime, ideally,
she should replace herself and then add some.

Evolution selects for the best adaptive traits to insure
that each female replaces herself within her lifetime, ideally, she should
replace herself and then add some.

Problems in the evolution of life history.

1. What is the best size or age to begin reproducing?

2. How many times should an individual reproduce?

3. How many eggs should there be per clutch?

4. How large should the eggs be?

5. When in the year should reproduction occur?

6. How to locate a mate?

7. How can young locate an appropriate habitat?

ULTIMATE CRITERION: produce maximum number of reproducing
offspring.

Factors influencing the production of maximum number of
reproducing offspring.

I. Biology of Individual

Size of adult

Principle of allocation

Egg size

II. Environmental Conditions

Biotic environment, coping with the other organisms in the
environment -competing with other organisms for food or shelter space,
etc.

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